Thermal battery electrolyte materials

ABSTRACT

An electrolyte composition can be capable of becoming molten when heated sufficiently. The electrolyte can include at least one lithium halide salt; and at least one lithium non-halide salt combined with the at least one lithium halide salt so as to form an electrolyte composition capable of becoming molten when above a melting point about 350° C. A lithium halide salt includes a halide selected from F and Cl. A first lithium non-halide salt can be selected from the group consisting of LiVO 3 , Li 2 SO 4 , LiNO 3 , and Li 2 MoO 4 . A thermal battery can include the electrolyte composition, such as in the cathode, anode, and/or separator region therebetween. The battery can discharge electricity by having the electrolyte composition at a temperature so as to be a molten electrolyte.

CROSS-REFERENCE

This patent application claims priority to U.S. Provisional ApplicationNos. 62/049,108 and 62/049,110 both filed on Sep. 11, 2014, which bothprovisional applications are incorporated herein by specific referencein their entirety.

GOVERNMENT RIGHTS

This invention was made with government support under W31P4Q-11-C-0044awarded by the U.S. Army. The government has certain rights in theinvention.

BACKGROUND

Thermal batteries are used in many military applications that have thepotential for an immediate or sudden demand for electric power. Thethermal batteries have proven to be essential for providing power forradar and electronic guidance, and are able to operate in the high spinand setback environment of artillery shells, and operate in the highshock experienced in an earth-penetrator weapon. They can remain inweapon systems for 25 years or more over a wide range of storage (−55°C. to 75° C.) without degradation, and should be hermetically sealed asthe moisture and air degrade the battery significantly.

Thermal batteries are operated at temperatures between 350-550° C. withmolten salt electrolyte. They are inactive at room temperature as themolten salt electrolyte is in a solid state bearing a low ionicconductivity for minimizing self discharge and degradation processes.This low conductivity phase of the electrolyte promotes the capabilityfor this type of battery to have very long shelf life with practicallyno capacity fade, and then can be activated within less than one second.For battery activation, internal pyrotechnics are ignited that generatethermal energy to raise the battery internal temperature to the meltingtemperature of the electrolyte, thereby causing a large increase in itsionic conductivity thus allowing the battery to operate. The battery isactive as long as the electrolyte is above its melting point (e.g.,typically above 350° C.) and generates power as long as enough activemass is available for the charge transfer reaction.

Previously, the most advanced common configurations of thermal batteriesfeature lithium-silicon alloy powder as anode material, FeS₂ as cathodematerial, and eutectic electrolyte such as LiCl—KCl or halideelectrolyte mixture of LiCl—LiF—LiBr. The configurations operates atvoltage less than 2 V and the capacity is limited, e.g., limited to 335mAh/g for LiSi alloy-FeS₂ redox couple. These configurations cannot meetthe requirements of new applications that are demanding high power andenergy density. The principal avenue for increasing thermal batteryspecific energy is to identify and develop new chemistry and electrodematerials, which provide high power with single cell voltages >2.5 V.The combination of higher specific capacity and higher operating voltagetranslates directly to higher power density at the battery level. Thebattery materials should be environmentally friendly, and potentiallyinexpensive in large scale production. As lithium alloyed with siliconor aluminum or tin provides high capacity as the anode, the power andcapacity of thermal battery depend upon the cathode material.

Therefore, it would be advantageous to have improved thermal batteriesthat overcome the shortcomings of prior thermal batteries.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and following information as well as other features ofthis disclosure will become more fully apparent from the followingdescription and appended claims, taken in conjunction with theaccompanying drawings. Understanding that these drawings depict onlyseveral embodiments in accordance with the disclosure and are,therefore, not to be considered limiting of its scope, the disclosurewill be described with additional specificity and detail through use ofthe accompanying drawings, in which:

FIG. 1 includes a graph that shows the voltage versus time for differentcathode materials.

FIG. 2 includes a graph that shows the experimental open circuit voltage(OCV) results of the LiSi—FeF₃ couple compared to the conventionalcouple of LiSi—FeS₂.

FIG. 3 includes a graph that shows discharge characteristics of athermal battery with LiSi/FeF₃ couple employing LiF—LiCl—Li₂SO₄ comparedto one with the conventional LiF—LiCl—LiBr electrolyte (Top:LiF—LiCl—Li₂SO₄; Bottom: LiF—LiCl—LiBr).

FIG. 4 shows an embodiment of a thermal battery.

FIG. 5 includes a graph that shows the heat flow (mw) versus temperaturein DSC for LiF—LiCl—Li₂SO₄ with 35-48-17.

FIG. 6 includes a graph that shows the discharge of CoF₃/CoS₂ cathodescompared to FeS₂ cathodes in a low current pulsed load test.

FIG. 7 includes a graph that shows the discharge of CoF₃/CoS₂ cathodescompared to FeS₂ cathodes in a current pulsed load test.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented herein. It will be readily understood that the aspects of thepresent disclosure, as generally described herein, and illustrated inthe figures, can be arranged, substituted, combined, separated, anddesigned in a wide variety of different configurations, all of which areexplicitly contemplated herein.

Generally, the present technology is related to thermal batteries andthe compositions and manufacturing thereof so as to have the potentialto provide immediate electric power upon a sudden demand for electricpower. The thermal batteries can have improved compositions at thecathode, anode, and/or electrolyte compositions in order to have theimproved functionalities. The thermal batteries can be used in equipmentto provide power and operate in the high spin and setback environment ofartillery shells, and high shock experienced in an earth-penetratorweapon, or other similar uses.

The thermal batteries can be configured with the cathode, anode, and/orelectrolyte compositions to be storage stable without degrading theelectrical power potential. For example, the thermal batteries can beconfigured with the cathode, anode, and/or electrolyte composition to becapable of being storage stable for up to 25 years or more over a widerange of storage (−55° C. to 75° C.) without degradation. The thermalbatteries can be hermetically sealed so that the cathode, anode, and/orelectrolyte compositions are not exposed to external moisture. This caninhibit degradation of the battery.

The thermal batteries can include the cathode, anode, and/or electrolytecompositions being configured to operate at temperatures between350-550° C. so that the electrolyte composition becomes a molten saltelectrolyte. As such, the thermal batteries can be inactive at roomtemperature and up to 100, 200 or 300 or to 350° C. as the saltelectrolyte is in a solid state and bearing a low ionic conductivity tominimizing self discharge and degradation processes. For example, thecathode, anode, and/or electrolyte compositions provide a lowconductivity phase at low temperatures for the electrolyte that promotesthe capability for this type of battery to have a long shelf life withpractically no capacity fade and then can be activated within less thanone second.

In one embodiment, the thermal batteries can include an ignition systemthat can increase the temperature to form molten electrolyte. Forbattery activation, the thermal battery can include internalpyrotechnics that can be ignited on a timer or on demand that generatethermal energy sufficient to raise the battery internal temperature toat least the melting temperature of the electrolyte, thereby causing alarge increase in the electrolyte ionic conductivity in order to provideelectricity. The thermal batteries can be configured to be active whenthe electrolyte is above the melting point (e.g., typically above 350°C.) and generate power as long as enough active mass is available forthe charge transfer reaction.

The thermal batteries can be configured to provide high power and energydensity. The cathode, anode, and/or electrolyte compositions can beconfigured to increase specific energy and provide high power. Thecathode, anode, and/or electrolyte compositions provide a combination ofhigher specific capacity and higher operating voltage resulting inhigher power density at the battery level. The cathode, anode, and/orelectrolyte compositions battery materials can be considered to beenvironmentally friendly and can be recycled or disposed of after use.

In one embodiment, an electrolyte that is solid and/or stable at lowtemperatures and molten at high temperatures can include: at least onelithium halide salt; and at least one lithium non-halide salt, whereinthe electrolyte includes a salt that has a melting point and can bemolten above 350° C. In one aspect, a first lithium halide salt caninclude a halide selected from F and Cl. In one aspect, a first lithiumnon-halide salt includes a salt selected from the group consisting ofLiVO₃, Li₂SO₄, LiNO₃, and Li₂MoO₄. In one aspect, the salt has a meltingpoint between 350° C. and 600° C., wherein said first lithium halidesalt includes LiF or LiCl, and said lithium non-halide salt includes atleast one salt selected from the group consisting of LiVO₃, Li₂SO₄,LiNO₃, and Li₂MoO₄. In one aspect, the salt includes a first lithiumhalide salt and a second lithium halide salt, such as LiF and LiCl aslithium halide salts together. In one aspect, the lithium non-halidesalt includes LiVO₃. In one aspect, the lithium non-halide salt includesLi₂MoO₄. In one aspect, the lithium non-halide salt includes Li₂SO₄. Inone aspect, the lithium non-halide salt includes LiNO₃. In one aspect,the electrolyte can include only lithium as a positive ion. In oneaspect, the electrolyte is at a temperature of between 350° C. and 600°C. and is molten. In one aspect, the amount of halide anion relative toa total amount of negative ions is at least about 20 mol %. In oneaspect, the first lithium halide salt and second lithium halide salthave a ratio of from about 0.1 to about 1.0. In one aspect, the totallithium halide salt and total lithium non-halide salt has a ratio offrom about 0.2 to about 2.0. In one aspect, the lithium halide saltbeing devoid of I or Br.

In one embodiment, a thermal battery can include electrolyte that issolid and/or stable at a low temperature (e.g., less than 350° C.) andmolten at the higher temperature (e.g., greater than 350° C.). Thethermal battery can include an anode; a cathode; and a separator havingthe potentially molten electrolyte. In one aspect, the cathode includesthe potentially molten electrolyte therein. In one aspect, the separatorhas an inorganic binder. In one aspect, the anode includes thepotentially molten electrolyte therein.

In one embodiment, a method of making a molten electrolyte can include:mixing at least one lithium halide salt with at least one lithiumnon-halide salt. In one aspect, such mixing can result in a potentiallymolten salt that is molten at 350° C. or above. The method can includecombining a binder with the potentially molten electrolyte.

In one embodiment, a method of providing electricity can include:providing an electronic device having a thermal battery with apotentially molten electrolyte of one of the embodiments; increasingtemperature to at least 350° C.; and discharging the thermal battery toprovide electricity.

In one embodiment, a thermal battery can include: an anode of lithiumalloy; a potentially molten salt electrolyte that is solid and/or stableat a low temperature (e.g., less than 350° C.) and molten at the highertemperature (e.g., greater than 350° C.); and a metal-fluoride cathode.In one aspect, the lithium alloy is lithium silicone or lithiumaluminum. In one aspect, the anode material can include 10%-50%electrolyte material. In one aspect, the metal of the metal fluoridecathode can include Fe, V, Cr, Mn, Co, or mixture thereof. In oneaspect, the metal-fluoride cathode can include FeF₃, or VF₃, or CrF₃, orMnF₃, or CoF₃, or a mixture thereof. In one aspect, the cathode materialcan include an amount of the electrolyte. In one aspect, the cathodematerial can include at least 65 wt % the metal-fluoride and at least 1wt % carbon material. In one aspect, the cathode material can include10%-50% electrolyte material. In one aspect, the metal-fluoride cathodecan include a carbon material therein. In one aspect, the carbonmaterial can be activated carbon, graphite, graphene, carbon nanotube,and combinations thereof.

In one embodiment, a thermal battery cathode can include FeF₃ or anyother material described herein, such as a hybrid material of FeF₃/FeS₂,CoF₃/CoS₂, and/or CoF₃/FeS₂. The cathode can further include a carbonmaterial, such as activated carbon, graphite, graphene, carbon nanotubes(CNT), or combinations thereof. In one aspect, the cathode can haveabout 0% to about 25% CNT and from about 75% to about 100% FeF₃ orFeF₃/FeS₂, CoF₃/CoS₂, and/or CoF₃/FeS₂ or other material such as ahybrid material, or any percentage within the percentage range. In oneaspect, the cathode can have about 5% CNT and about 95% FeF₃ or othermaterial such as a hybrid material. In one aspect, the cathode can havea dimension from about 0.1 mm to about 1.0 mm thick. In one aspect, thecathode can include a dimension from about 0.8 to about 0.1 mm thick. Inone aspect, the cathode can have a dimension of 0.5 mm.

In one embodiment, a method of making the thermal battery having a metalfluoride cathode can include combining the metal fluoride cathode into athermal battery. A method of making the metal fluoride cathode caninclude preparing the thermal cathode.

In one embodiment, a thermal battery cathode can include a metalfluoride selected from one or more of FeF₃, or VF₃, or CrF₃, or MnF₃, orCoF₃, or a mixture thereof, or any alone or in any combination.

In one embodiment, a method of providing electricity can includeproviding an electronic device having a thermal battery with a metalfluoride cathode; and discharging the thermal battery to provideelectricity.

FIG. 4 shows an embodiment of a thermal battery 100 that includes a heatpellet, a current collector above the heat pellet, a cathode region 106above the current collector, an electrolyte separator region 104 abovethe cathode region, an anode region 102 above the electrolyte separatorregion 104, and a second current collector above the anode region 102.

In one embodiment, the anode can be a lithium alloyed with silicon oraluminum or tin to provide high capacity as the anode. Corresponding thepower and capacity of the thermal battery can be improved by providingthe cathode material described herein with the electrolyte.

In one embodiment, the present technology includes a thermal batterywith a lithium silicon anode, a molten salt electrolyte, and afluorine-based cathode. In particular, the thermal battery can include afluorine-based cathode material that generates higher energy and powerdensities than conventional thermal batteries.

The thermal batteries can be configured to produce high power and energydensity thermal batteries with fluorine-based cathode. The thermalbattery employing the fluorine-based cathode materials can improve thepower density by more than three times compared to the conventionalones. A fluorine-based cathode of the present technology includes metalfluorides such as VF₃, CrF₃, MnF₃, FeF₃, and CoF₃ (see the Tables). In apreferred embodiment of the present technology, electrical conductingmaterials are incorporated into the fluorine-based cathode materials.

In one embodiment, a thermal battery can include a lithium alloy anode,lithium alloy eutectic electrolyte, and a metal fluoride cathode. It mayinclude an electrical conductor incorporated into the active component.The electrical conductor can be selected from the carbon-containingmaterials, such as activated carbon, graphite, and graphene, carbonnanotubes (CNT) or the like, such as any high surface area carbons.

It has been demonstrated that the thermal battery with the fluorinecathode materials showed improved performance. FIG. 1 shows dischargecharacteristics of a thermal battery with a LiSi/FeF₃ couple compared toone with a LiSi/FeS₂ couple. The LiSi/FeF₃ thermal battery showed OCV(i.e., open circuit voltage) of 3.3 V, while LiSi/FeS₂ showed OCV ofonly 2.2 V.

In one embodiment, the electrolyte can be a lithium halide. Thestability order of lithium halides is more preferred LiF>LiCl>LiBr>LiIto less preferred. However, molten salt electrolyte containing LiBr orLiI cannot be used for high voltage (>3.5 V) thermal battery operatingat 500° C., and thereby can be used at lower temperature applications,such as under 50° C. or 40° C. The LiF lithium halides may be used atany temperature range, such as above 400° C. or above 500° C. On theother hand, molten salt containing chlorine ion (e.g., LiCl) may not bedesirable as it is decomposed at 3.5 V.

In one embodiment, a battery can include: an anode of lithium alloy; amolten salt electrolyte; and a metal fluoride cathode. In one aspect,the battery can be a thermal battery. In one aspect, the lithium alloyis lithium silicone or lithium aluminum. In one aspect, the anode regionmay include 10%-50% electrolyte material. In one aspect, the molten saltcan include at least 20 wt % lithium fluoride and at least 40 wt %lithium chloride. In one aspect, the cathode material can include FeF₃,or VF₃, or CrF₃, or MnF₃, or CoF₃, or a mixture of them. In one aspect,the cathode material includes any amount of the electrolyte. In oneaspect, the cathode material includes at least 65 wt % of the fluorinecathode material and at least 1 wt % carbon material. In one aspect, thecathode region comprises 10%-50% electrolyte material. In one aspect,the carbon material is activated carbon, graphite, graphene, carbonnanotube, and the like.

The fluorine materials described herein can be used for high voltagecathode materials in thermal batteries. The cathode material can have aworking cell voltage that is greater than 30% of the traditional (e.g.,FeS₂) thermal battery cathode technology. This increased cell voltagecan allow for battery designs (e.g., battery housing) to become 20% to30% shorter in length. For example, in a high voltage 160 volt batterydesign, a battery using standard thermal battery technology wouldrequire approximately 84 cells a high voltage 160 volt battery design.Using cathode material described herein, only 64 cells would be neededfor a high voltage 160 volt battery design. The shorter length for thebattery designs can result in lower costs since there will be lessmaterial (fewer cells) required per battery. The shorter battery lengthcan also reduce the amount of battery mass and volume to fit in smallerspaces in devices or equipment.

Congruently, this technology can also be very beneficial for increasinga battery design's operating life within the same fit form factor as thecurrent design. Specifically, the room allotted to the now needlesscells could be taken up by thicker cells resulting in an increase to theoverall capacity of the battery design. Current production programs thatrequire block upgrades can benefit since more aggressive mission timescould be met while still maintaining the original fit form factor.Future space/kill vehicle applications can benefit from the ability toreduce the overall weight and volume of the power source.

In one aspect, the metal halide cathode can be combined with a moltensalt electrolyte stable up to 3.5 V, such as a lithium halide. Theelectrolyte provides two main functions: (1) maintain electrochemicalstability for high voltage operation (>2.5 V) and (2) effectivelyconducts lithium ions from the anode to the cathode. The thermal batterycan include lithium-metal halide redox chemistry between the cathode andmolten salt electrolyte, which results in a high capacity cathode forthermal battery that can generate high voltage (OCV>3 V) and as a resulthigh power and energy density.

The thermal battery can include metal halide composites that can producehigh cell voltage (>3.0 V) when coupled with a lithium alloy anode. Thecell voltage may be increased to >3.5 V by optimization. The thermalbattery described herein can operate at more than 2.5 V with currentdensity of 0.1-1 A/cm².

The thermal battery can include a molten salt electrolyte layersandwiched between high capacity anode and cathode. The lithium alloyanode is oxidized during the discharge process as:

M_(x)Li→M_(x)+Li⁺+e⁻  [1]

Where Mx is a metal alloyed with lithium, such as Sn or Si. Lithium ionLi+ diffuses through the molten salt electrolyte and reaches the cathodewhere it combines with the electron at the interface by the followingreaction:

M_(a)F_(b)+Li⁺+e⁻→LiM_(a)F_(b)  [2]

Where M can be V, Cr, Mn, Fe, Co, Ni, and Cu, as they can generate highdischarge capacity. These cathodes can generate >3.0 V open circuitpotential at the operating temperature of thermal battery. The a and bin Equation 2 can vary according to the chemical structures.

For anode materials, high capacity lithium-based materials arebeneficial. Lithium metal can provide the highest capacity. Lithiumalloyed with silicon and tin are qualified due to their high theoreticalenergy densities ˜4200 mAh/g and 994 mAh/g corresponding to the binaryalloys Li₂₂Si₅ and Li₂₂Sn₅. Li₂₂Si₅ (or Li_(4.4)Si) is a good candidatefor the anode as it produces highest emf (44 mV vs Li) among the alloys.Li₁₃Si₁₄ can be used as the anode. Discharge states for the anode are:

Li₂₂Si₄→Li₁₃Si₁₄→Li₇Si₃→Li₁₂Si₇  [3]

The particle size of lithium alloy can be reduced by high energy ballmilling. The technology includes particle size control, optimum anodecomposition (electrode and electrolyte), and pellet size and itsthickness optimization.

Molten salt composed of metal halide and sulfate, such as LiF—NaF—KF,LiF—LiCl—Li₂SO₄ and/or LiF—Li₂SO₄, can be used in the high voltagecathode region. Their melting point is relatively high (>400° C.) andstable at high voltage.

Molten nitrates have much lower melting point than molten halides andtheir conductivities are comparable to those of halides. For example,LiNO₃-NaNO₃ (56-44, mol %) melts at 187° C. and ionic conductivity is1.14 S/cm at 327° C. The ionic conductivities of LiCl—KCl andLiF—LiCl—LiBr are 1.69 and 3.21 S/cm at 475° C., respectively. Thenitrate-based electrolyte may be used effectively for the thermalbattery at much lower temperature (Table 1).

During the discharge process, the nitrate is reduced to oxide andnitrite as:

2Li⁺+LiNO₃+3e ⁻→LiNO₂+Li₂O(s)  [4]

The insoluble Li₂O film prevents the nitrates from further reduction andallows the electrochemical window of 4.5 V for molten LiNO₃ at 300° C.and LiNO₃—KNO₃ eutectic. The Li₂O film protects the lithium anode byforming the interface in the oxidizing nitrate electrolytes. Thepresence of Cl-ions in the thermal battery components can be excluded inone aspect because the ion can breakdown the protective Li₂O film duringthe discharge process:

Li₂O_((a))+Cl⁻→2Li+OCl⁻  [5]

High concentration of lithium ions can be helpful for highly conductiveelectrolyte. Nitrate melts that do not contain LiNO₃ as a majorcomponent, such as NaNO₃—KNO₃ melts, may not be as beneficial forlithium-based anodes, and thereby can be excluded. High stability of theprotective Li₂O film can be achieved by increasing the LiNO₃ componentof the molten salt.

TABLE 1 Proposed Molten Salt Electrolytes for High Capacity CathodesElectrolyte Composition (mol %) M.P. (° C.) LiCl—KCl 58.8-41.2 352-354LiF—LiCl—LiBr 22-31-47 430-444 LiF—NaF—KF 46.5-11.5-42 455 LiF—Li₂SO₄41-59 530 LiCl—Li₂SO₄ 60.5-39.5 485 MiNO3—KNO3—CsNO3 37-39-24 97LiNO₃—KNO₂ 40-60 108 LiNO3—NaNO3—KNO3 37.5-18-44.5 120 LiNO₃—KNO₃ 42-58124 LiNO₃—LiNO₂ 30-70 147 LiNO3—RbNO3 30-70 148 LiNO3—CsNO3 57-43 174LiNO₃—NaNO₃ 56-44 187 NaNO₃—KNO₃ 46-54 222

The molten nitrate electrolytes are compatible with high-voltage cathodematerials. The use of nitrate salts as a lower melting electrolyte mayshorten thermal battery's activation time and reduces the weight of heatsources and insulation. Among the nitrates, LiNO₃—KNO₃ and LiNO₃—NaNO₃are expected to generate high discharge current at high voltage (>3.0V).

The cathode with the combinations described herein (e.g., LiSi/FeF₃) canprovide higher capacity than the current state of the art cathodes. Asseen in FIG. 1, energy density with LiSi/FeF₃ was increased by 3.3 timesat 1 V cutoff compared to the conventional cell with FeS₂ andLiF—LiCl—LiBr. Accordingly, the thermal batteries can be devoid of theelectrolyte being LiF—LiCl—LiBr because of a lack of stability atvoltages higher than 3V.

A high voltage (>3 V) lithium sulfate electrolyte can provide cell withthe cathode and electrolyte shows discharge voltage more than 2.2 V at100 mA/cm². It has been found that performance of the cell can depend oncathode, ball milling time, and additives to the cathode. Also, theperformance of the thermal battery may be improved further through theoptimization of the electrode and electrolyte and their processingconditions.

Nanoscale particles can be used for efficient utilization of the activeelectrode materials and ionic and electron conductive additives can beincorporated into the cathode to further enhance the dischargecharacteristics at high rate.

In one embodiment, a cathode can include a LiSi—FeF₃ couple or otherLiSi-metal-fluoride couple. FIG. 2 shows the experimental open circuitvoltage (OCV) results of the LiSi—FeF₃ couple compared to theconventional couple of LiSi—FeS₂. The LiSi—FeF₃ couple generated higherpotential (e.g., 3.4 V vs. lower 2.2 V with LiSi—FeS₂) and can producehigh energy density (712 mAh/g vs. present 335 mAh/g with LiSi—FeS₂) at1 V cutoff. Thus, FIG. 2 shows the open circuit voltage duringactivation: Top line (lighter) FeF₃, Bottom line (darker) FeS₂.Fluorine-based cathode material such as FeF₃ is coupled with LiSi anodeto generate high voltage thermal battery; it demonstrates open-circuitvoltage of 3.3 V with operating cell voltage more than 2.5 V at 100mA/cm² current density. FIG. 2 shows a 50% improvement in OCV withLiSi—FeF₃ compared to LiSi—FeS₂. Table 2 shows the open current voltagefrom some embodiments.

TABLE 2 Capacity of Proposed Cathodes Capacity, OCV at Cathode ChemistryV_(cutoff) = 1 V 500 C. FeS₂ FeS₂ + 3/2Li⁺ + 3/2e− → 1/2Li₃Fe₂S₄ 1206 A· s/g 2.2 V (1.5Li/FeS₂) CoS₂ FeS₂ + 4/3e− → 1/3Co3S4 + 2/3S²⁻ 1045 A ·s/g 2.2 V (1.5Li/FeS₂) FeF₃ FeF₃ + 3Li⁺ + 3e− → Fe + 3LiF 2565 A · s/g3.4 V (3Li/FeS₂) CoF₃ CoF₃ + 3Li⁺ + 3e− → Co + 3CoF 2496 A · s/g 3.4 V(3Li/FeS₂)

In one embodiment, various of the described molten salt electrolytes canbe for use in thermal batteries. In particular, ternary or quaternaryelectrolyte material that is electrochemically stable at high voltage(>3 V) can be used.

The molten salts described herein are solid at normal temperature, wherethe electrolyte has no ion conductivity and therefore thermal battery isnot active. However, when the electrolyte is heated to high temperature,the electrolyte achieves a molten state, becoming an excellention-conductor. Thus, thermal battery becomes active under hightemperature.

In one aspect, the present thermal battery can include an electrolytecomposition having two or three or more salts. In one aspect, the saltscan contain lithium only as the positive ion, and in this aspect noother positive ions except lithium are included. The lithium salts caninclude two types of negative ions; one is halide, and the other isnon-halide. In one aspect, the salts with halide negative ion are F— andCl—. In one aspect, the non-halide negative ions include vanadate,sulfate, nitrate, and molybdate. In a preferred embodiment of presentinvention, the electrolyte has one or more salt with halide and one ormore with non-halide.

The thermal battery can also include a separator composition having theelectrolyte and an inorganic binder. Examples of the inorganic bindercan include magnesium oxide, silica, and zirconia.

Also, the electrode regions can be configured to have the ability tocontact or contain the electrolyte for use in thermal batteries.

FIG. 3 shows discharge characteristics of a thermal battery withLiSi/FeF₃ couple employing LiF—LiCl—Li₂SO₄ compared to one with theconventional LiF—LiCl—LiBr electrolyte (Top: LiF—LiCl—Li₂SO₄; Bottom:LiF—LiCl—LiBr). The thermal battery with the new LiF—LiCl—Li₂SO₄ showedhigh voltage and stable voltage traces, while the thermal battery withLiF—LiCl—LiBr electrolyte showed low voltage and unstable dischargecharacteristics. LiF—LiCl—LiBr electrolyte in the high voltage electrodemay react with the electrodes, or dissolve the electrode, or decomposesat high voltage (>3V) due to Br− ions in the electrolyte. The newelectrolyte can easily be synthesized by melting process of individualcomponents.

In one aspect, a molten salt includes two types of salt; a first lithiumsalt and a second lithium salt, said molten salt having a melting pointbetween 350° C. and 600° C., wherein said first salt includes LiF, LiCl,and said second salt includes at least one salt selected from the groupconsisting of LiVO₃, Li₂SO₄, Li₂MoO₄. In one aspect, the positive ion islithium only. In one aspect, an amount of halide anion relative to atotal amount of negative ions included in said molten salt is 20 mol %or more.

A thermal battery can include at least one unit cell including apositive electrode, a negative electrode, and an electrolyte disposedbetween said positive electrode and said negative electrode, whereinsaid electrolyte includes the molten salt in accordance with thedisclosure herein. In one aspect, at least one of said positiveelectrode and said negative electrode further includes said molten salt.

The battery can include a stack of 2 cells to about 500, more preferablyfrom about 4 cells to about 250 cells, and most preferably from about 8cells to about 200 cells.

The battery can include an anode having a thickness of about 0.01 mm toabout 2 mm, more preferably from about 0.05 mm to about 1.5 mm, and mostpreferably from about 0.1 mm to about 1.0 mm.

The battery can include a cathode having a thickness of about 0.01 mm toabout 2mm, more preferably from about 0.05 mm to about 1.5 mm, and mostpreferably from about 0.1 mm to about 1.0 mm.

The battery can include an electrolyte separator region thickness ofabout 0.01 mm to about 2 mm, more preferably from about 0.05 mm to about1.5 mm, and most preferably from about 0.1 mm to about 1.0 mm.

The present disclosure provides improved electrolyte material for use inthermal batteries including the cathodes and anodes thereof. The ways inwhich the improved electrolyte, cathode, anode, and battery overcome theshortcomings of the prior art are discussed in more detail below.

One aspect of the present disclosure is directed to an electrolytematerial for use in thermal batteries, in one optional aspect theelectrolyte material being substantially binder-free. Examples ofbinders that can be excluded can include yttrium oxide.

The electrolyte material can include at least about 20 wt % lithiumfluoride, at least about 20 wt % lithium chloride, and at least about 25wt % Li₂SO₄. In one aspect, the material includes from about 10 to about20 wt % lithium fluoride, from about 5 to about 20 wt % lithiumchloride, and from 10 to about 30 wt % Li₂SO₄.

The electrolyte material includes at least about 20 wt % first lithiumhalide, at least about 10 wt % second lithium halide, and at least about20 wt % lithium non-halide. In one aspect, the material includes fromabout 10 to about 30 wt % first lithium halide, from about 10 to about30 wt % second lithium halide, and from 10 about to about 30 wt %lithium non-halide.

The electrolyte material includes at least about 10 wt % lithiumfluoride, at least about 10 wt % lithium chloride, and at least about 20wt % Li₂SO₄. In one aspect, the material includes from about 10 to about20 wt % lithium fluoride, from about 10 to about 20 wt % lithiumchloride, and from about 10 to about 30 wt % Li₂SO₄.

The electrolyte material includes at least about 5 wt % first lithiumhalide, at least about 5 wt % second lithium halide, and at least about5 wt % lithium non-halide. In one aspect, the material includes fromabout 5 to about 10 wt % first lithium halide, from about 5 to about 10wt % second lithium halide, and from about 5 to about 10 wt % lithiumnon-halide.

The electrolyte material includes at least about 5 wt % lithiumfluoride, at least about 10 wt % lithium chloride, and at least about 20wt % Li₂SO₄. In one aspect, the material includes from about 3 to about30 wt % lithium fluoride, from about 3 to about 30 wt % lithiumchloride, and from about 3 to about 30 wt % Li₂SO₄.

The electrolyte material includes at least about 5 wt % first lithiumhalide, at least about 5 wt % second lithium halide, and at least about10 wt % lithium non-halide. In one aspect, the material includes fromabout 5 to about 10 wt % first lithium halide, from about 5 to about 10wt % second lithium halide, and from about 5 to about 10 wt % lithiumnon-halide.

In a specific example, the electrolyte material includes about 5 wt %first lithium halide, about 5 wt % second lithium halide, and about 10wt % lithium non-halide. In one example, the electrolyte materialincludes at least about 3 wt % lithium halide, and at least about 3 wt %lithium non-halide. In one aspect, the material includes from about 3 toabout 10 wt % lithium halide, and from about 3 to about 10 wt % lithiumnon-halide.

In one example, the cathode material includes at least about 3 wt %metal fluoride, and at least about 0.1 wt % high surface area carbon. Inone aspect, the material includes from about 2 to about wt 5% metalfluoride, and from about 0.001 to about 1 wt % high surface area carbon.In one example, the cathode material includes at least about 10 wt %metal fluoride, and at least about 3 wt % high surface area carbon. Inone aspect, the material includes from about to about 20 wt % metalfluoride, and from about 1 to about 10 wt % high surface area carbon. Inone example, the cathode material includes at least about 20 wt % metalfluoride, and at least about 1 wt % high surface area carbon. In oneaspect, the material includes from about 30 to about 10 wt % metalfluoride, and from about 0.5 to about 3 wt % high surface area carbon.

The electrolyte may contain three or four salts such as those describedherein. The lithium sulfate in the recited amounts can be substitutedwith a similar amount of a different lithium non-halide salt, such asthose described herein.

With the new metal fluoride cathode, the inventors determined a problemwith the previous electrolytes breaking down due to the enhancedperformance. Now, the inventors have identified the lithium halide andlithium non-halide electrolyte (e.g., binary with only one lithiumhalide or tertiary with two different lithium halides) to handle thevoltage without breaking down. If binary, it can be preferably LiCl orLiF, or using both when tertiary.

In one example, the electrolyte can be LiF—LiCl—Li₂SO₄ approximateweight percentages. FIG. 5 shows the heat flow (mw) versus temperaturein DSC for LiF—LiCl—Li₂SO₄ with 35-48-17. The composition of theelectrolyte can change the viscosity and melting temperature. Somenon-limiting examples of LiF—LiCl—Li₂SO₄ can include the followingratios: 25-48-27; 30-48-22; 35-48-17; or 40-48-12, or approximate weightpercentages. The melting point (° C.) was determined as follows:LiF—LiCl—Li₂SO₄, such as at the following ratios: 25-48-27 at 436.2° C.;30-48-22 at 433.6° C.; or 35-48-17 at 434.3° C. In one example, LiF canrange between 10-50%, LiCl can range between 30-60%, and LiSO₄ can rangebetween 15-45%.

The present disclosure provides improved cathode material for use inthermal batteries and batteries including the material. Cathodes inaccordance with the present disclosure and batteries containing suchcathodes are generally characterized by enhanced conductivity, increasedvoltage, and/or longer lifetime as compared to conventional cathodes andbatteries.

The cathode technology can also include a hybrid cathode of two or morematerials of the same type, such as combinations of two or more of themetal fluoride cathode materials described herein. In one aspect, thiscombination can be FeF₃ and/or FeF₃+CNT with another material of thesame type. The fluoride based cathodes have a higher impedance thantheir sulfur based cathodes. However, the addition of CNTs into thecathode material can improve the overall impedance of the cathode, butthey do not improve energy handling capability. Accordingly, the CNTscan added to the material in small amounts (e.g., less than or about 5%,or 4-6%, or 3-7% or 2-8%).

In one aspect, the hybrid material can provide higher instantaneouspower (or current) compared to the individual materials alone. Thehybrid material can be a combination of the fluoride and sulfide basedcathodes, and thereby include a fluoride and a sulfide. The hybrid canprovide an improved combination of energy and power. Examples of thehybrid material can include FeF₃/FeS₂, CoF₃/CoS₂, and/or CoF₃/FeS₂. Theratio of the foregoing materials in the hybrid can be (e.g., FeF₃/FeS₂)is in a 50/50 ratio, or 25/75 ratio, or 75/25 ratio, or 20/80 ratio, or80/20 ratio, or 10/90 ratio, or 90/10 ratio, or any ratio therebetween.In one aspect, the CoF₃/CoS₂ can be preferred.

FIG. 6 shows the performance of the hybrid material CoF₃/CoS₂ comparedto FeS₂. The studies were conducted with a current pulsed profile. Thedischarge voltage of CoF₃/CoS₂ cathodes is higher by about 0.8 V toabout 1.0 V than that of the FeS₂ cathode. FIG. 7 shows the discharge ofCoF₃/CoS₂ cathodes compared to FeS₂ cathodes in the current pulsed loadtest where the discharge voltage of developed CoF₃+CoS₂ cathode at 250mA/cm² is 1 V higher (e.g., 2.35 V vs. 1.28 V) than that of FeS₂cathode, and where cell impedance of CoF₃+CoS₂ Cathode is 2.36 timeslower than that of FeS₂ cathode.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Additional featuresmay also be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

In one aspect, the thermal batteries can be devoid of one or more of:lithium-silicon alloy powder as anode material; FeS₂ as cathodematerial; or the eutectic electrolyte being LiCl—KCl or halideelectrolyte mixture of LiCl—LiF—LiBr. The configurations of the thermalbatter so not include the components for a LiSi alloy-FeS₂ redox couple.

It should be understood that discussion of the molten electrolyte refersto the potential of the electrolyte to become molten at the temperatureranges provided herein. The electrolyte in the battery is not molten atlow temperatures, such as common storage temperatures, and that theelectrolyte becomes molten upon reaching the melting temperature. Forexample, the electrolyte may be a solid that does not flow at a storagetemperature or when the heat pellet is not ignited. However, theelectrolyte becomes molten and flowable upon reaching the meltingtemperature, such as when the heat pellet is ignited.

One skilled in the art will appreciate that, for this and otherprocesses and methods disclosed herein, the functions performed in theprocesses and methods may be implemented in differing order.Furthermore, the outlined steps and operations are only provided asexamples, and some of the steps and operations may be optional, combinedinto fewer steps and operations, or expanded into additional steps andoperations without detracting from the essence of the disclosedembodiments.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated herein, will be apparent to those skilled in the art from theforegoing descriptions. Such modifications and variations are intendedto fall within the scope of the appended claims. The present disclosureis to be limited only by the terms of the appended claims, along withthe full scope of equivalents to which such claims are entitled. It isto be understood that this disclosure is not limited to particularmethods, reagents, compounds compositions or biological systems, whichcan, of course, vary. It is also to be understood that the terminologyused herein is for the purpose of describing particular embodimentsonly, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). In those instances where a convention analogous to “atleast one of A, B, or C, etc.” is used, in general such a constructionis intended in the sense one having skill in the art would understandthe convention (e.g., “a system having at least one of A, B, or C” wouldinclude but not be limited to systems that have A alone, B alone, Calone, A and B together, A and C together, B and C together, and/or A,B, and C together, etc.). It will be further understood by those withinthe art that virtually any disjunctive word and/or phrase presenting twoor more alternative terms, whether in the description, claims, ordrawings, should be understood to contemplate the possibilities ofincluding one of the terms, either of the terms, or both terms. Forexample, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” and the like include the number recited andrefer to ranges which can be subsequently broken down into subranges asdiscussed above.

Finally, as will be understood by one skilled in the art, a rangeincludes each individual member. Thus, for example, a group having 1-3cells refers to groups having 1, 2, or 3 cells. Similarly, a grouphaving 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and soforth.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims. All references recited herein are incorporated hereinby specific reference in their entirety, including: U.S. Pat. No.8,394,520; U.S. Pat. No. 8,440,342; and U.S. Pat. No. 8,652,674. Inthese references, the cathode can be substituted for the metal-fluoridecathode described herein, and/or the molten electrolyte be substitutedfor the molten electrolyte described herein.

1. An electrolyte composition capable of becoming molten comprising: atleast one lithium halide salt; and at least one lithium non-halide saltcombined with the at least one lithium halide salt so as to form anelectrolyte composition capable of becoming molten when above a meltingpoint about 350° C.
 2. The electrolyte of claim 1, wherein a firstlithium halide salt includes a halide selected from F and Cl.
 3. Theelectrolyte of claim 2, wherein a first lithium non-halide salt includesa salt selected from the group consisting of LiVO₃, Li₂SO₄, LiNO₃,Li₂MoO₄.
 4. The electrolyte of claim 1, wherein the electrolytecomposition has a melting point between 350° C. and 600° C., whereinsaid first lithium halide salt includes LiF or LiCl, and said lithiumnon-halide salt is selected from the group consisting of LiVO₃, Li₂SO₄,LiNO₃, and Li₂MoO₄.
 5. The electrolyte of claim 1, comprising a firstlithium halide salt and a second lithium halide salt.
 6. The electrolyteof claim 5, comprising LiF at the first lithium halide salt and LiCl asthe second lithium halide salt.
 7. The electrolyte of claim 1,comprising only lithium as a positive ion.
 8. The electrolyte of claim1, wherein the lithium non-halide salt includes Li₂MoO₄.
 9. Theelectrolyte of claim 1, wherein the lithium non-halide salt includesLi₂SO₄.
 10. The electrolyte of claim 1, wherein the lithium non-halidesalt includes LiNO₃.
 11. The electrolyte of claim 1, wherein an amountof the halide anion relative to a total amount of negative ions is atleast about 20 mol %.
 12. The electrolyte of claim 5, wherein the firstlithium halide salt and second lithium halide salt have a ratio of fromabout 0.1 to about 1.0.
 13. The electrolyte of claim 1, wherein thetotal lithium halide salt and total lithium non-halide salt has a ratioof from about 0.2 to about 2.0.
 14. The electrolyte of claim 1, thelithium halide salt being devoid of I or Br.
 15. The electrolyte ofclaim 1, wherein the electrolyte is within one or more of an anode,electrolyte separator, or cathode.
 16. The electrolyte of claim 1, theelectrolyte composition including LiF—LiCl—Li₂SO₄.
 17. The electrolyteof claim 1, the electrolyte composition including LiF—LiCl—Li₂SO₄, whereLiF can range between 10-50%, LiCl can range between 30-60%, and LiSO₄can range between 15-45%.
 18. A thermal battery comprising: an anoderegion; a cathode region; and the electrolyte composition of claim 1capable of becoming molten when above a melting point about 350° C. 19.The thermal battery of claim 18, wherein the cathode region includes theelectrolyte composition therein.
 20. The thermal battery of claim 18,wherein the anode region includes the electrolyte composition therein.21. The thermal battery of claim 18, comprising a separator regionbetween the cathode region and anode region that includes theelectrolyte composition therein.
 22. The thermal battery of claim 18,comprising a separator region between the cathode region and anoderegion that includes the electrolyte composition and an inorganicbinder.
 23. A method of providing electricity comprising: providing anelectronic device having a thermal battery of claim 18, wherein theelectrolyte composition is at a temperature so as to be a moltenelectrolyte; and discharging the thermal battery to provide electricity.